I. Field of the Invention
The present invention relates to a multiple spindle data disc system which is used in connection with a computed tomography X-ray scanner having a plurality of detectors, a source of X-rays movable relative to the detectors, and a memory unit which receives data from the detectors in source fan format.
II. Description of the Prior Art
Fourth generation computed tomography (CT) X-ray scanners produce data organized in source fans which must be reorganized into detector fans before this data can be used effectively in an image processing reconstruction algorithm. More specifically, in FIG. 1 there is illustrated a source of X-rays 10 and a ring 12 of detectors D.sub..0. through D1999. Source 10 is movable with respect to detectors D.sub..0. through D1999. In any given position, source 10 generates a fan of X-rays 14 which strike a limited number of detectors, for example detectors D.sub..0. through D999. Fan of X-rays 14 in the course of reaching detectors D.sub..0. through D999 also passes at least in part through a target 16. Thus, the output of detectors D.sub..0. through D999, with source 10 in the illustrated position of FIG. 1, provides a first "source fan format" of data representing the content of target 16.
As mentioned above, source 10 is movable with respect to detectors D.sub..0. through D1999. For example, source 10 may revolve in a clockwise direction with detectors D.sub..0. through D.sub.1999 being stationary. When source 10 reaches a new position, the output of the detectors in ring 12 is observed as providing a new set of data in source fan format. More specifically, as illustrated in FIG. 1, a second fan of X-rays 18 may be generated when source 10 assumes a subsequent location 20. In subsequent location 20, fan 18 strikes detectors D.sub.N through D.sub.999+N.
Of course, source 10 may revolve in an orbit which is the same diameter, larger than, or smaller than the diameter of ring 12. Moreover, source 10 may be stationary and ring 12 rotate. Still further, source 10 might take the form of a stationary ring, and the position at which X-rays are emitted rotate about that ring. All that is required is relative motion between the source of X-rays and a plurality of detectors.
As source 10 completes a full revolution, a plurality of samples are generated in detectors D.sub..0. through D.sub.1999, one sample for each position of source 10.
The output of detectors D.sub..0. through D.sub.1999 may be stored in a standard disc drive. A standard disc drive, for example, may comprise a package of ten memory storage discs stacked one above the other, thereby providing twenty disc surfaces for storage of data. With one surface dedicated to location control, nineteen disc surfaces are available for memory storage. Each surface may, for example, be divided into 800 tracks with each track divided into 32 sectors. A cylinder is typically defined as including one track from each of the 19 surfaces, each located above or below another so that each such conventional disc drive has 800 cylinders with 19 tracks per cylinder.
If each sector has 512 bytes of 8 bits each, and data words are generated from each detector D.sub..0. through D.sub.1999 of 16 bits in length, each sector has the capacity of storing 256 such data words.
Accordingly, the data from detectors D.sub..0. through D.sub.1999 illustrated in FIG. 1 as source 10 is moved one complete revolution may be stored on such a prior art disc drive in the manner illustrated in FIG. 2. More specifically, if each cylinder has 19 usable tracks (surfaces) and each track has 32 sections, and each section is capable of storing 256 16 bit detector data words, then each cylinder is capable of storing approximately 150,000 detector data words. If approximately 1000 detectors are involved in each sample, then approximately 150 samples of 1000 detectors each can be stored in each cylinder. Accordingly, as shown in FIG. 2, cylinder number .0. may be used to store data for detectors D.sub..0. through the highest number detector employed in sample 150, and subsequent cylinders 1, 2, 3, . . . 20 are used to store data from detectors involved in subsequent sample numbers 151-300, 301-450, 451-600, and so on. In this manner, data from on the order of 3000 source fans may be effectively stored in a prior art disc drive.
However, as before mentioned, it is necessary that data organized in source fan format be reorganized into detector fan format before such data can be effectively used in an image processing reconstruction algorithm. The term "detector fan" format may be explained with regard to FIG. 3, in which source 10 is shown illustratively located in a plurality of source positions S.sub.1 through S.sub.8 and detectors D.sub.N and D.sub.N+1 are illustrated along detector ring 12. Also shown is target 16. For purposes of explanation (but not limitation), source 10 is assumed to begin in a position S.sub.1 and revolve in a clockwise direction through position S.sub.8. In positions S.sub.1 through S.sub.7, source 10 provides information for detector D.sub.N. In positions S.sub.2 through S.sub.8, source 10 provides information for detector D.sub.N+1. The collection of data from detector D.sub.N with source 10 in positions S.sub.1 through S.sub.7 is data organized in a "detector fan" format. Likewise, data from detector D.sub.N+1 with source 10 in positions S.sub.2 through S.sub.8 is data organized in a "detector fan" format for detector D.sub.N+1.
With regard to FIG. 2, accordingly, detector fan format data is illustrated as a horizontal sampling of data for any particular group of detectors for each of cylinders .0.-19. Accordingly, to obtain a detector fan format of data from a disc drive having data stored as illustrated in FIG. 2, each of cylinders .0.-19 must be interrogated. However, to move from one cylinder to another on a disc drive requires physical movement of the disc drive head and, therefore, requires a substantial amount of time. In addition, the process of selecting particular data from each cylinder required to accumulate a detector fan format of data for a particular group of detectors requires substantial memory and data processing capability.